Steam-volatile Esters and Lactones

Terpene esters constitute an important compound class in the essential oils. Acetate esters are those most frequently encountered more rarely, formates, propionates, butyrates, valerates and caprylates. Experience accumulated with over 30 different esters of lower fatty acids, shows that the zones on silica gel G layers, when developing with benzene or chloroform, are about 2.5 times higher than those of the corresponding alcohols (chamber saturation). Brud and Daniewski [28] have confirmed our finding [260] for loose silica gel layers also. The largest differences in hRf-values have been observed when using normal saturation (NS). 

Solvents I = benzene, II = trifluorotrichloroethane-methylene dichloride (60 + 40) III = chloroform. 

Comparison of the i /-values of terpene esters of homologous lower fatty acids shows that the values increase with increasing number of carbon atoms [120]. They approach a limiting value asymptotically [7, 251]. Formates are exceptional since they appear at the level of the propionates (Table 24) and can be separated only from acetates when using benzene or chloroform as solvent. 

The intramolecular esters, the lactones, may be mentioned here. The antihelminthic agent santonin, for example, belongs to this class. A well known lactone is coumarin, the odour of which resembles dried woodruff and which is found in numerous essential oils, also as derivatives. SuND and Saccabdi [273] have succeeded in separating 5 cou-marins on silica gel G layers, using petroleum ether (50—75° C)-ethyl acetate (67 + 33) or n-hexane-ethyl acetate (72 + 29). The sequence found was coumarin, 6-methylcoumarm, dihydrocoumarin, 3-methylcoumarin, 3-ethylcoumarin. 

Korte and Vogel [140] have chromatographed lactones, lactams and thiol-actones of organic chemical interest. They used standard conditions on silica gel G layers with diisopropyl ether, ethyl acetate and isooctane alone and in mixtures. 

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